Laboratory weathering of special laminated glasses for renovating the roof of an industrial monument

View of test specimen during the sprinkling phase to generate high temperature load changes.

The rain is bucketing down, then suddenly the dark clouds begin to clear and the sun peeps out: the British climate is known for its “moods.” This changeability must also be taken into account when carrying out building work – such as a project to renovate an historic factory building, in which the usability of the roofing had to be ensured. The roof surface was fully glazed and covered an area of almost 4,000 m². For heritage conservation reasons, the appearance was to be preserved, while the heat insulation had to be modernized to meet today’s building standards. The specialist planners stipulated that thermal insulation glazing be used as sun protection, with glass fitted on the outside and a fleece inlay. To ensure the durability of the glass structure, several original-size glazing sheets were to be installed at a roof slope of 55 degrees and – in accordance with DIN EN 12543 – exposed to compressed-time weathering for 2,000 hours. This means exposure to radiation with elevated UV levels, cyclical sprinkling, and switches between temperatures from minus 10 to plus 50 degrees Celsius.

Fraunhofer IBP was able to implement the client’s testing requirements to the letter. After all, the researchers have a lot of know-how in constructing solar simulation installations. Usually the standards prescribe insolation fields of 1 square meter in area and with an irradiance of 900 W/m2. With larger areas, as in this case over 4 m², overlapping effects arise, and the irradiance is uneven over the entire glass component. Consequently, the researchers at Fraunhofer IBP developed a calculation program that enables surfaces of several square meters in area to be irradiated evenly. Because the customer had specified a temperature cycle of four hours, the temperature switchovers in the climate chambers had to be quick. This is scarcely possible with larger chambers. As a solution, the scientists divided the testing area into two parts and provided the test specimens with a transparent cover, such that a narrow air duct was created in front of the specimen. Using ducts that could be switched from “summer” to “winter,” as it were, in just a few seconds via motorized flaps, the researchers connected both testing areas to the air supply units.

After the experiments, the scientists not only carried out visual inspections of the glass components, but also opened up the edge bond and carried out gravimetric testing to determine whether water had been absorbed. In this way, they were able to demonstrate without doubt that the test specimens were tight.